Technical Field
The present invention concerns a method of operating a wind power installation as well as a wind power installation and a wind park having a plurality of wind power installations.
Description of the Related Art
Wind power installations and methods of operating same have long been known. FIG. 1 shows by way of example such a wind power installation having a pylon with a pod and a generator. The pod includes a rotor with rotor blades which are moved by the wind to generate electric current with the generator.
Usually wind power installations are used to convert kinetic energy from the wind into electrical energy and to feed it in the form of electric current into an electric network which also in simplified form can be referred to as an electric mains or just mains. Nowadays wind power installations have become established and can also be used to support the electric network. In particular wind power installations which provide for feeding electric current into the network by way of an inverter are distinguished by their capability of being able to react very quickly to changes in the network.
Depending on the respective situation in the network, network support can mean for example that a wind power installation or correspondingly a wind park with a plurality of wind power installations reduces the power to be fed into the network if there is an in particular short-term excessive supply of energy in the network. Conversely, the wind power installation or the wind park can also feed additional power into the power network in a very short-term fashion in expectation of a short-term lack of supply of energy, that is to say in particular in expectation of a short-term, in particular abrupt rise in power consumption, that is to say the power is utilized. That is possible for example in that, with that expectation, the wind power installation or the entire wind park is operated at reduced power, that is to say prior to the expected event less power is fed into the network than would be possible on the basis of the design of the wind power installation in question and the prevailing wind.
Initial proposals for network support have been set forth for example in laid-open application DE 100 22 974, also published in U.S. Patent Publication 2003/155773. In accordance therewith it was proposed that the fed-in power is reduced in dependence on the frequency in the network, which can be an indicator of oversupply or undersupply of power in the network. Such a power reduction however suffers from the disadvantage that the power reduction means that less power is fed into the network than is available in the prevailing wind. In other words, power is thrown away. The wind power installation operators are frequently entitled to receive remuneration for that thrown-away power or at least to receive corresponding compensation. For example, under the Renewable Energy Law (EEG) from the year 2000 in Germany with subsequent adapting alterations a network operator is obliged to provide recompense for power available from regenerative energy sources like wind power installations.
In the case of wind power installations therefore there is the problem of precisely determining the available power because the network operator does not want to provide excessive remuneration nor does the wind power installation operator want to receive too little remuneration. A wind power installation which feeds less power into the network than is available from the prevailing wind is however operated in a reduced mode. The optimum operating point at which so much power is taken from the wind prevailing at that time is thus a notional operating point in the case of the wind power installation operated in a reduced mode.
In principle an optimum operating point can be associated with each wind speed. It will be noted however that this presupposes accurate measurement of the wind speed, which for various reasons is frequently a theoretical, at least extremely inaccurate option. A modern wind power installation has a large rotor diameter. For example the E126 from Enercon has a rotor diameter of 126 m. In that case the rotor sweeps over an area of about 10,000 sq. m (m2). There is in practice not a uniform wind speed over those 10,000 sq. m—quite apart from gusts and other variations in wind speed with time. At the same time a rotor diameter of 126 m also means a difference in height of the swept region of 126 m. The use of a wind speed measurement procedure for determining the available power of the wind power installation in question is therefore at least problematical, if not even inappropriate. In the case of a hub height of 137 m there is a difference of height at which the rotor is operative of 74-200 m. Basically the rotor of a wind power installation is the sole suitable means for detecting the relevant speed.
In general attention is directed to DE 103 00 733 B3, EP 2 275 674 A2, DE 100 22 974 A1 and DE 10 2010 026 299 A1.